Terminal devices rejoining the network

Hello, I have a question about terminal devices rejoining the network.After the terminal equipment has joined the network, the coordinator and electricity when the terminal equipment from sleep wake up, terminal equipment will rejoin the network, but due to the coordinator is gone, it will appear to rejoin terminal network failure events, but why will appear for about 20 seconds to rejoin the network failed events?I wonder if the terminal is constantly rejoining the network?And I don't find code in infrastructure code routine 1217 that continues to rejoin the network after a failed rejoin event.